Air propeller



Nov. 26, 1.935. HOFFMANN' El AL 2,021,999

' AIR PROPELLER Filed 'June 25, 1934' 4- Sheets-Sheet 1 I /v va /woes A TTORNEJ I I I. lv Nov. 26, 1935. 1.. HOFFMANN ET AL 2,021,999

AIR PROPELLER Filed June 23, 1934 4 Sheets-Sheet 3 M Hg. 5 37 39 38 V I /N VEN/26 AI TORNEJ/ Nov. 26, 1 935. 1.. HOFFMANN ET AL 2921;999-

AIR PROPELLER Filed June 23, 1954 Sheets-Sheet 4 //v VENTOIQSY A T TOR IVE) Patented Nov. 26, 1935 PATENT OFFICE An PROPELLER Ludwig Hoflmann and Manfred Grabarse, Berlin- Hermsdorf, Germany, assignors to Gustav Schwarz G. m. b. H., Berlin-Waidmannslust, Germany, a'llmited company of Germany Applicationlune 23, 1934, Serial No. 732,11

In Germany June 24, 1933- 14 Claims.- (Cl. 170-162) Our invention relates to improvements in air propellers, and more particularly in air propellers of the type in which the blades are adapted to be automatically set about their axes in different positions in accordance with avariable condition of operation, such as the velocity of flight, the number of revolutions, the dynamic air pressure, or the static air pressure, the said propellers comprising a regulating system in which a setting power depending upon the'said variable facerted for example by a spring, and the tension of the spring counteracting the centrifugal force is such that according to the number of revolutions the system is set in different positions of equilibrium.

The object'of the improvements is to provide a propeller of this type in which the blades are not subject to disturbing forces adapted to movethe same out of the correct positions to which they have been set. Such disturbing forces are produced in a high degree in the operation. Apart from friction the variable moment of'the forces .of the air on the blades acts as a disturbing force, further, elastic deformations of the blades,

undesired variations of the tension of the springs or other resetting members, for example, by

fatiguing, etc.

Another object of the improvements is to provide a propeller in which the blades are in a stable state of regulation, so that they are not made to oscillate about their axes by the setting and resetting devices continuously moving the same beyond the correct position and returning the same into an initial position.

.With these and other objects in view our invention consists in constructing the regulator so that the blades are held in stable equilibrium in several "positions. (Thus, the setting of the blade from one of the said positions into an adjacent one iseflected only when the variable factor of the operation, for example the numberof I'GVOIH? =tions, has passed upwardly or downwardly beyond a certain value, the said values being different from each other by a definite measure. Since the regulator is thus always in stable equilib- I rium independently of the position of the blades (except at the moments when setting takes place), the influence of the disturbing forces is obviated, because the stabilizing forces are chosen so that they largely exceed the disturbing forces. The substitution of continuous regulationby step-wise regulation practically causes no disl0 advantages as might be assumed at first sight. For on the one hand the number of the steps may be enlarged when it is desired that the regulation approximates continuous regulation. On the other hand practical operation requires 15 that the pitch of the propeller be not continuously varied in accordance with the number of revolutions, the velocity of flight or other con. ditions, because frequently it is desired for example to fly within a certain range of velocity with the highest pitch of the propeller, for example during a touring flight with throttled en- .gine, in order to obtain comparatively high velocity. with low motor effect. In practical operation substantially only two positions of the pitch of the propeller are needed, one for ascending flight, and theother one for velocity flight. Accordingly it is suflicient to construct the regulator for two positions of the blades. For special purposes particularly for a flight at 3 great height a third step may be provided.

In describing the invention reference will be made to a regulating system depending on the number of revolutions of the propeller, a centrifugal body or bodies and a spring orsprings 85 counteracting the same being provided for setting the blades in'position. But we wish it to be understood that our invention is not limited to regulation in dependence of velocity nor to the use of a" centrifugal body andfsprings for' setting the blades. f I

For the purpose of explaining the invention. several examples embodying the some have been shown in the accompanying drawings in which the same reference characters have been used in all the views to indicate corresponding parts. In said drawings,

Fig. 1 is' anelevation partly in section showing the propeller in a somewhat diagrammatical way,

Fig. 2 a diagram,

Fig. 3 is a sectional elevation of the hub of a propeller, the figure showing a practical embodimentof the invention,

Fig. 4 is an elevation partly in section of the hub shown in Fig. 3,

Fig. 5 is a sectional elevation showing a hand operated 'device controlling the setting mechanism,

Fig. 6 is an elevation showing the propeller and the device controlling the setting mechanism as mounted on an air craft,

Fig. 7 is a sectional elevation showing a modification of the apparatus shown in Fig. 3,

Fig. 8 is an elevation showing a measuring device, I

Fig. 9 a detail sectional elevation taken on the line 9-9 of Fig. 1, and

Fig. 10 is a fragmentary sectional elevation similar to the left hand part of Fig. 7 and showing a modification.

Fig. 1 shows diagrammatically one of the blades 1 of an air propeller. The axis of the propeller, ordinarily the shaft of the engine, is represented by a line 2-2. In the construction shown in Fig. 1 the blades are adapted to be set into two different positions. The blade I is adapted to'be turned about its axis 3 indicated in Fig. 1 by a point, for varying the pitch. The position illustrated in full lines corresponds to 'a small pitch of the propeller, and the position shown in dotted lines corresponds to a larger pitch. To the blade an arm 4 is secured which carries at its end a weighted body 5 acted upon by the centrifugal force C indicated in the figure by an arrow. To a pin 6 provided at the outer end of the arm 4 a link I is jointed which is connected with its other end to a pin 8 carried by a rod 9 formed with a shoulder l0 and a collar H, and acted upon by a coiled spring l2. In the position shown in the figure the collar ll bears on a shoulder I3 of the body of the hub, while the collar I0 is spaced from a nut l3 which for the present may be assumed to be fixed in position.

The operation of the system is as follows:

While the propeller is at rest the centrifugal force C is zero, and the force exerted by the spring It, sets the blades into the position of small pitch shown in full lines, the collar II bearing on the shoulder l3 of the hub. Whenthe propeller rotates the force C acts on the weighted body 5, which force acts in opposition to the force S of the spring. When the force C has attained a value which exceeds the power of the spring the weighted body 5 and thereby the blade I are turned about the axis 3 into the position of high pitch shown in dotted lines and so far that the shoulder H) of the rod 9 bears on the nut l3. Thereby the power of the spring is increased by compression, which, however, has no influence on the setting operation, because simultaneously the length of the lever through which the force of the spring acts on the blade is reduced in a higher degree, because in the original position the spring acts on the blade through a length of lever l, and in the second position only through a lever of the length l, the angular position of the link 1 relatively to the axis 2, 2 being varied by the movement of the arm 4. Further, while the weighted body 5 is being displaced the centrifugal force I rises by reason of the increase of the radius r to r.

The conditions are illustrated in detail in the diagram shown in Fig. 2, in which the moments Ms exerted by the force 8 of the spring and the moments Mc exerted by the centrifugal 'force C have been plotted as ordinates from the line of abscissae representing the number of revolutions n. 5 At first the blades of the propeller may be in the position of small pitch. As the number of revolutions n is increased the centrifugal force rises according to the curve I. The moment produced in this position of the blade by the 10 spring has the value Ms which is independent of the number of revolution. If the moments of the spring and the centrifugal force become equal as is indicated by the point A the blade is turned about its axis 3 into the position shown in Fig. 1 in dotted lines. By the reduction of the length of the lever of the spring from Z to l' the moment of the spring is reduced to the value Ms2, while simultaneously the centrifugal force rises by the radius being increased from r to 1" (Figure 1), so that now the centrifugal moment follows the curve II. If the number of revolutions rises above the value corresponding to the point A, the blade remains in the position of large pitch. This is also the case when the number of revolutions is reduced. Resetting does not take place already when a value of the number of revolutions is attained which corresponds to the point A, but only when the centrifugal moment Me! has fallen off to the value of the reduced moso ment Ms2 ofthe spring. In Fig. 2 the point B corresponds to the returning of the blade into the position of low pitch.

If now the number of revolutions rises again along the curve I setting takes place when the forces have the value represented by the point A as has been described.

In both positions the blade is always in stable equilibrium, and forces of definite size are needed for bringing the same out of its position. This is one of the essential differences between the air propeller of this invention and automatically set air propellers of known constructions, which have continuous regulation, and in which therefore the blade is always in indifferent equilibrium in which infinitely small forces are sufllcient for throwing the same out of its position.

The characteristic change of the setting operations in dependence of the number of revolutions, which appears from Fig. 2, corresponds to ulation, as appears from the following:

puring take ofl and climbing the number of revolutions of the propeller is comparatively small and it is below the value corresponding t the point A. Therefore the propeller is in the position of small pitch which corresponds to the requirements of climbing. If after having attained the desired height the air craft is set for flying level, the number of revolutions rises beyond the point A by reason of the reduction of the resistance. When the number of revolutions has passed beyond the point A the blade is set into the position of small pitch, which corresponds to the requirements of flying at high velocity. when beginning the touring flight the pilot may throttle the engine, so that the number of revolutions slightly falls off without the position of the blade corresponding to the velocity flight being changed, because setting would take place only at the point B, and therefore the range of the numbers of revolutions included between the points A and B is at the disposal of tine pilot for throttling. v7

Only if-the number of revolutions falls below the value corresponding to the point B, for exalmost completely throttles the engine, the blades are jointed one for each of the blades.

are set into the initial position of small pitch, and therefore into the position needed for a new start or for an ascending flight which may be necessary by reason of the landing operation having failed.

In the practical embodiment shown in Figs. 3 and 4 the blades I, which are rockable about the axis 3, 3 in opposite senses, are mounted in sleeves l4 made in two sections, which sleeves are mounted for being turned about their axis in antifriction bearings I5 of the body of the hub 90. Each of the sleeves [4 has a ring I 6 fixed thereto, which is connected or made integral with laterally projecting arms 4 the outer ends of which carry the weighted bodies 5 and have the links I jointed thereto. The said bodies are located in Fig. 4, respectively above and below the plane in which the axes 2-2 and 33 are located, as will be understood from Fig. 3. Frequently a separate weighted body may be dispensed with, because the eccentric mass of the arm 4 produces a sufficient centrifugal moment. On the arm 4 or on the weighted body 5 additional weighted bodies l8 may be provided for imparting another characteristic curve to the regulator. In an axial bore 19 made in the body 13 ofthe hub a sleeve 20 is longitudinally shiftable which is made integral with two eyes 2| disposed at. opposite sides of the sleeve, and to the said eyes the links 1 Within the sleeve 20 there is a coiled spring 22 which bears with one end on a ring'23 and with its other end on an inwardly directed flange 24 provided within the hub 99 at the end of the bore l9. The

- said spring tends to shift the sleeve 20 towards of the spring 22 into the position of large pitch. In Fig. 3 the" positions of one of the weighted bodies have been indicated respectively in full lines and in dashes and dots.

In bores 25 located laterally and at opposite sides of the bore l 9 pistons 26 are shiftable which are rigidly connected'by rods 21 with the eyes 2| of the sleeve 20. The movement of the pistons is limited by bushings 28, 29 fitted within the bores 25. The chambers provided between the said bushings and the pistons 26 may be filled with oil, and the pistons 26 are provided each i with a longitudinal bore 39 through which the oil is pressed when the'pistons are being set, the apparatus being used for damping or braking the movement of the pistons 26 and the blade setting mechanism connected therewith. In the construction shown in Fig. 3 the bushing 29 is located within a tubular extension of the bushing 28?, and both bushings are formed with external screw-threads? and 29' by means of which they are adjustable longitudinally of the bore 25 for varying the stroke of the piston and therefore the angle at which the blades are set. By mounting the bushing 29 within the bushing 28 both bushings may be moved simultaneously and in the same direction by turning the bushing 28, so that the distance between the opposing faces of the bushings remains constant, and both bushring 23 is prevented by a key and groove 3|.

ings may be turned so that the distance between the said faces is altered. Asthe positions of the said opposing faces of the bushings control the pitch of the blades, the said pitch to which the blades are set in the end positions may be varied. The ring 23 may be rigidly connected with the sleeve 29. However, in the construction shown in Fig. 3 it is shiftable longitudinally of the sleeve 20, so that the tension of the spring 22 may be varied. For this purpose it is mounted on a sleeve 33, and the sleeve 33 and the ring 23 are provided with interengaging screw-threads 32. The sleeve 33 is rotatable but not shiftable within the sleeve 20, and rotary movement of the The sleeve 33 may be turned by hand by means of a key engaging in holes 34. Thus the ring 23 may be shifted inaxial direction for varying the tension of the spring 22.

' Within the sleeve 20 there is a tubular rod 35 which is connected with the said sleeve through the intermediary of an antifriction bearing 36, so that it is movable with the said sleeve in axial direction without, however, taking part in the rotary movement of the axis 2, 2 of the propeller. The rod 35 is connected in a suitable way with a device which as is shown in Fig; 6 is mounted near the seat of the pilot, andwhich is used for regulating the stroke of thesleeve 29 and the setting of the blades by hand. This device may be constructed in the manner shown in Fig. 5. As shown, the rod 35, or a flexible shaft 35' posisleeve 31 which is provided internally with screwthreads 38 engaged by a pair of bushings 39 and 49, and which is fixed to a suitable part near the seat of the pilot. The bushing 39 is con' nected with the shaft 35' by means of groove and key 4| so that it takes part in the rotary movement of the shaft but is shiftable relatively thereto. Atits inner end the bore of the bushing is enlarged at 42 so that a collar 43 provided on the shaft 35' may pass into the same. The axial movement of the bushing 39 turning in the screw-threads of the sleeve 38 is limited by a bushing 44 and by the end. face of the bushing 40. On the free end of the shaft 35 a crank is loosely mounted which is equipped tively connected therewith, is passed through a ateither side of its hub 46 with claws'4l and 48 adapted for engagement with corresponding claws 49 provided respectively at the end of the shaft 35' and at the end of the bushing 40 projecting from the sleeve 31. The bore of the bushing 49 is enlarged at its inner end and the enlarged portion is adapted to be engaged by the collar 43. The shoulders 50 and 5| within the bushings 39 and 40 provide stops for the axial movement of the shaft 35', and they determine the positions of the blades by reason of the positive connection of the'said shaft with the sleeve 29. By means of the crank 45 the bushings 39 and 40 may be displaced at will. When the crank 45 is turned while it is in the position and when thecrank 45 is shifted towards the end '52 of the shaft 35 and with the claws 41 and 49 into engagement with each other, rotary movement of the crank, the shaft 35' and the bushing 40 causes axial displacement of the bushing 39. The shoulders 50 and 5| of the bushings 39 and 40 provide the end stops for the displacement of the sleeve 20, and therefore they control the setting of the blades.

1 shown in the figure in which the claws 48 and 49 are in engagement with each. other, the bush-- ing 49 is screwed into or out of the sleeve 31,

While by means of the apparatus shown in Fig. 5 the pitches to which the blades are set in the end positions may be varied at will, by varying the tension of the spring by means of the ring 23 the number of revolutions at which setting takes place may be varied at will.

The construction may be such that the blades are adapted to assume not only two, but three or more positions in which they are in stable equilibrium. This result is obtained for example by providing a subsidiary spring or springs which are made effective when the blades being set are in intermediate positions, and which increase the spring power counteracting the'centrifugal force of the weighted bodies l8 by a definite value. In the construction shown in Fig. '7 concentrically of the spring 22 a second coiled spring 53 is provided which bears with one end on a flange 54 formed on a sleeve 58 and with the other end on a disk 55. For the present the sleeve 58 and the flange 54 may be assumed to .be rigidly connectedwith the sleeve 28. The

disk is shiftable on a rod 51 formed with a head 55 providing an end stop and rigidly connected with the sleeve 58. The flange 24 on which the spring 22 is supported is extended inwardly so far that it provides a stop for the disk 55. I

The propeller may be in the position of small pitch. If the number of revolutions is increased so far that the centrifugal force compensates the power of the spring 22 the sleeve 20 is shifted in the manner described above within the bore I! while compressing the spring 22. However before the end of the stroke of the sleeve 28, the

disk 55 engages the flange 24, so that the power of the spring counteracting the centrifugal force is materially increased by the spring 53 being added to the spring 22. Only after the centrifu-- gal force has further risen to a definite-value in which it is able to overcome the forces of both springs, further setting to the end stop takes place. Fig. '7 shows the three different positions of the weighted body 5.

with the setting operation is compensated.

The action of the spring 53 may be regulated at will by varying the tension thereof. Such regulation may also be automatically made, for example in dependence of theair pressure.

For this purpose in Fig. 7 a piston 88 is shiftable coaxially of the sleeve 28 in a hollow cylindrical extension 58, which piston is locked against rotary movement by a rod 82 connected therewith and extending in a bore ii of the sleeve 20.

T0 the said piston a spindle 88 having screw- 58 and a variation of the distance between the threads 64 of large pitch is secured. The piston encloses a chamber. 65 which is closed from all sides in an air-tight way and which is filled with air under. atmospheric pressure. When the air craft rises to greater heights the outer atmospheric pressure falls off, so that the piston BI] is forced outwardly by the air-confined within the l a chamber 85. Therefore the piston always assumes a position corresponding to the outer; air

pressure. I L

The spindle 83 is in engagement with the sleeve 58 which heretofore was assumed to be rigidly connected with ,the sleeve 20, which, however, really is adapted to be turned relatively thereto in screw-threads 66. When the sleeve 58 is turned the spring 53, its stop 55 and the bolt 51 are turned and axially shifted according to the pitch of the screw-threads 86. Thereby the distance between the stop 55 and the flange 24 is varied.

If the piston 69 is shifted inthe manner described according to the outer air pressure the spindle 83 which is formed with screw-threads of large pitch causes rotary movement of the sleeve parts 24 and 55. The senses of the pitches of the screw-threads 84 and 66 are such that upon a reduction of the pressure of the outer air and accordingly outward movement of the piston 60,

the distance between the stops 55 and 24 is re- 39 duced. However, the smaller the said distance is, the lower is the number of revolutions at which the blade is set into the position of highest pitch. This corresponds to the practical requirements of the flight at great height.

The shiftable piston 89 may be replaced with a 'diaphragm as has been indicated in Fig. 10,-

where the diaphragm has received the reference character 9|. In the construction shown in Fig.

7 two springs are provided which are successivelythrown into operation. Thus the blade has three positions of stable equilibrium. But we wish it to be understood that our invention is not limited to the use of three springs only.

The total range of regulation may be subdi- 5 vided into several steps also in another way, asv is shown diagrammatically in Figs- 1 and 9. As has been remarked above, the ring l3 acts as a stop for the shoulder l0 when the centrifugal force shifts the rod 9 downwardly while compress- 50 ing the spring. Heretofore the nut I3 has been assumed to be fixed in position. As-a matter of fact it is axially shiftable, and it is provided externally with screw-threads 88 of large pitch. On an arm 8| rigidly connected therewith a 5 weighted body 82 is mounted which is subjected to centrifugal force. In Fig. 9 the centrifugal force acting thereon has been indicated C. A spring 84 attached to a relatively fixed point 83 and to the lever 8| tends to turn the nut l3 in 60 Fig. 9 in clockwise direction. If the centrifugal force C rises to a value exceeding the spring power, the-weighted body 82 gets into the position shown in Fig. 9 in dotted lines. Thereby the spring is somewhat put under tension, and 65 simultaneously the length of the lever through which the spring acts is considerably reduced. Therefore the weighted body 82 and the nut I8 remain in the new position until the centrifugal force has attained a value which is so small that 70 the moment exerted thereby is not suflicient any more to overcome the power of the spring. Now the nut l3 returns into the initial position shown in full lines with a number of revolutions of the propeller which is below the number of revo1u--.75

tions at which the first setting operation took place. The movement of the arm 8| in either direction is limited, by stops 8! shown diagrammatically in Fig. 9.

With the rotary movement of the ring l3 an axial displacement is connected, so that the stop for the shoulder I 0 changes its position. The parts have such dimensions and arrangement that upon an increase of the number of revolutions setting of the weighted body 82 takes place only after the weighted body 5 with the link I and the rod 9 have been set, and when the shoulder Ill bears on the nut Hi. When the nut I3 is set the stop for the shoulder l0 gets into a lower position, and the centrifugal force acting at the point 6 moves the blade into a. third position in which the pitch is still larger than in the position shown in Fig. 1 in dotted lines.

For exactly testing the spring power in a simple way the apparatus illustrated in Fig. 8 is used. It consists of an oil-filled drum 61 with diaphragm 68 and a manometer 69, which drum is placed on the front side 10 of the sleeve-20. At the opposite side a ball 12 provided with a pressure screw H is fixed in a suitable way, for

example to the eyes 13 of the body of the hub.

By screwing the screw II down the size of the tension of the spring may be read from the manometer 69.

While in describing the invention reference has been made to particular examples embodying the same we wish it to be understood that our invention is not limited to the constructions shown in the accompanying drawings and that various changes may be made in the general arrangement of the apparatus and the construction of its parts without departing from the invention. For example in the construction shown in Fig. 1 the moment of the centrifugal or setting force C is increased and the moment of the resetting force exerted by the spring 12 is reduced when the weighted body moves from the position shown in full lines into the position shown in dotted lines. We wish it to be understood that our invention is not limited to this specific construction, the essential feature being that under the said conditions themoment of the resetting force is reduced relatively to the moment of the setting force.

We claim:

1. An air propeller, comprising a hub, a blade mounted thereon and adapted to be turned about its axis, and mechanism operatively connected with said blade for turning the same about its axis and comprising a device-controlled by a variable factor of the operation for exerting a setting force and a device for exerting a resetting force thereon, said mechanism being constructed so as to have its parts changed in position by the action of said devices in such a way that the effect of the resetting force relatively to that of the setting force is changed in a'sense opposite to the change of the setting force.

2. An air propeller, comprising a hub, a blade mounted thereon and adapted to be turned about its axis, mechanism operatively connected with said blade for turning the same about its axis and comprising a device controlled by a variable factor of the operation for exerting'a setting force and a device for exerting a resetting force thereon, said devices being connected with each other by a link inposition for having its angular position changed by the relative movements of said devices in a sense for varying the effect of the 3. An air propeller, comprising a hub, a blade mounted thereon and adapted to be turned about its axis, mechanism operatively connected with said blade for turning the same about its axis and comprising a device controlled by a variable factor of the operation for exerting a setting force and a device for exerting a resetting force thereon, said devices acting respectively on a 1 member having rectilinear movement and on a member pivotally mounted and connected with each other by a link located so that the distance between the saidlink or its extension and the pivot varies according to the relative position 1 of said devices, and stops limiting the relative movement of said devices.

4. An air propeller, comprising a hub, blades mounted thereon and adapted to be turned about their axes, mechanism operatively connected with 2 said blades for turning the same about their axes and comprising devices for exerting setting and resetting forces thereon, one of said devices comprising a shiftable member and a spring having initial power and acting on said member and 2 the other one comprising a member connected with said blades and movable towards and away from the direction of the movement of the first named member, a link connecting said members and stops limiting the end positions of said mech- 3 anism.

5. An air propeller as claimed in claim 1, in

.which the device for exerting resetting force blade and formed with shoulders, stops cooperating with said shoulders for limiting axial movement of said rod, and means for shifting said stops towards and away from said shoulders.

- '7. An air propeller, as claimed in claim 1, in which the device exerting resetting force comprises power exerting members which are successively made operative, and in which automatic 4 means controlled by a variable factor are provided for varying the conditions under which the said members are made operative.

8. An air propeller as claimed in claim 1, comprising in addition stops for limiting the movement of said mechanism, and automatic means controlled by a factor of service for shifting one of said stops.

9. An air propeller as claimed in claim 1, comprising in addition means for braking said mech- 5 anism.

10. An air propeller as claimed in claim 1,- comprising in addition means for measuring said resetting force.

11. An air-propeller comprising a mounted thereon and adapted to be turned about its axis, and automatic mechanism adapted to be operated by a variable factor of service for turning said blade about its axis and having several positions of stable equilibrium, the said mechanism being constructed so that the forces acthub, a blade 13. An air propeller as claimed in claim 11, comprising in addition stops for limiting the pitch of the said blade in either direction, and means for varying the positions of both stops independently or each other and in the direction or the movement of said mechanism.

f4. An air propeller as claimed in claim 11, comprising in addition stops for. limiting the pitch of the blade in either direction, and means for varying the positions of both stops independently of each other and in either sense in the direction of the movement of said mechanism.

LUDWIG I- IOFFMANN. MANFRED GRABARSE. 

